The question of who the best of the Sahaabah was has always been a thorny issue within the Ummah, especially among the Ahl al-Sunnah wa al-Jamaa’ah. Even the Sahaabah disputed with one another over the topic.
Expectedly, most of the Ahl al-Sunnah consider Abu Bakr to have been the best of the Sahaabah, then Umar, then Usmaan, and then Ali. By contrast, the Shiah believe that Ameer al-MomineenAli was the best, then al-Hasan, then al-Husain, and then Sayyidah Faatemah (a.s.). There is a minority among Sunnis —including some Sahaabah and a lot of Sufis —who share the Shiah view on the matter.
So, it is a very big issue, and provokes the deepest emotions of some people. In fact, countless Shiahs and others have been murdered for more than a millenium by Sunni extremists, only for their belief in the superiority of Ali.